Systems, devices and methods for controlled jetting of individual droplets of viscous medium, e.g. solder paste or glue, onto a substrate, e.g. an electronic circuit board, are known in the art. See for instance patent publications U.S. Pat. No. 6,450,416; US 2002/0043570; US 2002/0047052; US 2002/0014602; US 2002/0015780; US 2004/0118935; US 2004/0262824; US 2005/0092774; US 2005/0167519; and WO 2005/048678, which are all incorporated herein by reference.
In the MY500 Jet Printer provided by Mydata automation AB, a system for jetting viscous medium comprises a jet printing machine, a solder paste tube for containing solder paste to be jetted, a residue receptacle for holding residue and surplus of solder paste resulting from the jetting process, an ejector element for performing the actual jetting of the solder paste, and a holder matable with the jet printing machine. The holder, jetting element, residue container, and solder paste tube are arranged to be assembled away from the jet printing machine, and to form an individual, aggregate unit which may be readily positioned in a matable holding elements provided in the jet printing machine. The ejector comprises a feeder in the form of a feed screw, which is powered by a stepper motor arranged in the holder matable via interface of the stepper motor and the ejector.
In US 2004/0217193, also incorporated herein by reference, there is disclosed a jetting device and a method for improving the performance of the jetting device. The jetting device comprises a jetting outlet through which droplets are jetted, and gaseous flow is provided past the jetting outlet such that an adverse effect on the performance of the jetting device is prevented, the adverse effect resulting from the accumulation of viscous medium residue at the jetting outlet. In other words, the provision of a gaseous flow past the jetting outlet results in a transportation away from the jetting outlet of viscous medium residue that otherwise might adhere to the walls of an outlet nozzle, and cause detrimental viscous medium build-up that may have a negative impact on the overall jetting performance.
Even though the jetting apparatus disclosed in US 2004/0217193 represents a significant improvement in relation to prior jetting apparatuses, a variation in the quality or performance of the jetting process over time has been found. Therefore, a need exists for even further improving the jetting method and apparatus disclosed in US 2004/0217193.